A heart-sound detecting apparatus, including a heart-sound microphone which detects at least one heart sound produced by the heart of a living subject and outputs a heart-sound signal representing the detected heart sound, a time-frequency analyzing device for analyzing, with respect to time and frequency, at least a portion of the heart-sound signal that includes a first heart sound I, and an aortic-valve-opening-timing determining device for determining a timing when the aortic valve of the heart opens, based on a time when a magnitude of the analyzed signal at a frequency higher than a frequency range of a main component present in an initial portion of the first heart-sound I is greater than a prescribed threshold value.